DESCRIPTION (Applicant's abstract): Gap junctions are clusters of intercellular channels, composed of connexin proteins, that connect the cytoplasm of adjacent cells, allowing the direct transfer of small molecules. In the vascular wall, three connexins are expressed (Cx37, Cx40, and Cx43) which may mediate communication among endothelial cells, smooth muscle cells, and between endothelial cells and smooth muscle cells. The long-term goal of this project is to understand the role that gap junction communication plays in regulating vascular responses and to define the contributions of specific connexins. It is thought that vascular communication is an important pathway for coordination of vasomotor responses, by allowing for transfer of electrical and/or chemical signals. Two viable connexin knockout mouse lines (Cx37KO and Cx4OKO mice) and a line deficient in both connexins (Cx37/40K0) were previously generated, allowing a test of the role of specific connexins in vascular communication and function. In this study, intracellular injection of gap junction-permeable tracers is used to track changes in endothelial, myoendothelial, and smooth muscle communication in connexin knockout versus wild-type blood vessels, while whole-cell voltage clamp is performed to compare ionic coupling. The possibility that Cx37 and Cx4O interact to form heteromeric channels is investigated in cell culture by transfection of connexin expression vectors and by single channel recordings. The role that Cx37 and Cx40 play in vasomotor responses is examined by performing isometric tension measurements on wild-type and connexin knockout aortic rings treated with a vasodilator or a vasoconstrictor. The possibility that Cx37 and/or Cx40 contribute to myoendothelial gap junctions and mediate endothelium-dependent, NO-independent relaxation responses is investigated. Because gap junctions may be important in maintaining vascular homeostasis and responsiveness, a better understanding of vascular intercellular communication could lead to new insights and treatments for atherosclerosis, hypertension, and types of angina caused by vasospasm of coronary vessels.